Prefabricated trusses are often used in the construction of building structures because of their strength, reliability, low cost, and ease of use. The trusses are typically assembled in a factory using machinery for mass-fabrication of individual truss components. The trusses are assembled, for example, on large assembly or setup tables and then shipped to construction sites.
A prefabricated truss typically includes truss members coupled by nailing plates. Each truss member has a first surface and a second surface, and the truss members are pre-cut for a pre-defined truss configuration. Trusses may be fabricated to span large distances. For example, 30, 60, or 100 feet span distances are not uncommon. Fabricating such large trusses necessitates the use of multiple setup tables. A single work surface would require an unusually large table and would require the workers to crawl onto the table work surface or to reach extremely long distances to correctly position the truss members and nailing plates on the table work surface. Multiple setup tables arranged in a row with isles between the tables permit workers to walk between the tables to position the truss members on the work surfaces of the tables to reduce crawling onto the work surface of the tables. The isles between setup tables also facilitate removal of the trusses from the setup tables after production.
In assembling trusses, truss members are arranged on truss assembly setup tables, and nailing plates having nail like projections or teeth extending from one side are placed at the intersections of the truss members with their teeth pointed toward the first and second surfaces. The plates are then pressed into the truss members using, for example, a roller or a vertical press. Typically, a gantry press is used to embed the nailing plate teeth into the truss members, moving along the row of spaced setup tables and pressing the nailing plates into the truss members forming trusses. In some lines one large truss may be assembled over several tables, or several trusses may be setup on the tables and then the gantry press rolls over the line of tables pressing the nailing plates into the truss members of the several trusses.
Modern gantry presses include a gantry frame that travels on two tracks mounted to the floor along opposite sides of the truss table. Typically, light crane rail tracks are used. A vertical press or a roller press may be mounted to the gantry frame at a predetermined distance above a truss table work-surface so that as the gantry frame moves along the tracks, the nailing plates are pressed into the truss members.
The installation of the gantry press tracks is critical in the proper operation of the gantry press. In a typical installation, the tracks are spaced away from the sides of the truss tables to provide adequate clearance for the gantry press frame. Since the gantry press rides on the tracks, the tracks must be level and true with respect to each truss table work-surface. Due to the size and weight of the gantry press, the tracks must be securely fastened to the floor and made of a suitable material, typically, steel. During use of a truss table, an operator places the truss members and nailing plates on the truss setup tables work-surface, requiring the operator to step over the tracks to access the isles between the setup tables, or stand farther from the table and extend the truss members and nailing plates an additional distance. The tracks may become tripping hazards or impede worker movement and thus worker productivity. Due to the size and spacing of the tracks, easy access to the truss table work-surface and areas between the truss tables is impeded and throughput is reduced.
One attempt to overcome some of the above described problems is a trackless roller press described in assignee's co-pending patent application Ser. No. 08/951,116, now U.S. Pat. No. 5,933,957. The trackless roller press eliminates the floor track to allow workers closer access to the setup table, but the roller press cannot traverse from table to table in a line of multiple, spaced truss setup tables. The roller press described in patent application Ser. No. 08/951,116, now U.S. Pat. No. 5,933,957 attaches to a single truss setup table.
It would be desirable to provide a gantry press apparatus which enables fabrication of trusses without requiring that tracks be placed on the floor next to the truss setup tables to permit unimpeded access to the truss tables and the isles between the truss tables. It would also be desirable to provide an apparatus which moves easily from one truss table to the next in an assembly line of multiple, spaced tables.